A mining process or method is the summation of methods through which, starting from a deposit, metals and/or metallic compounds of commercial purity and quality are obtained, in a profitable manner and with an acceptable environmental impact.
In the known leaching process, one or many mineral values contained in an ore or a concentrate are dissolved, generally using an aqueous solution of a leaching agent. The term can also be extended to include dissolving secondary materials, such as scrap metals, residues, and waste.
Leaching produces an aqueous solution rich in extracted ions of the valued metal (PLS, pregnant leaching solution) from which it is possible to separate this metal and recover it with a high level of purity. Also, a solid residue or gravel is produced, that, ideally, has a sufficiently low level of valued leached minerals, as to discard it in tailings or dump.
If the solid leaching residue is impregnated with salts or precipitates that eventually can release toxic agents once exposed to the environment, before discard, the residue must be properly treated in order to achieve elimination or stabilization of the potentially contaminant compounds. In some cases, leaching can have a different objective than the one previously described. For example, when a concentrate is leached for selectively extracting certain impurities, and leaching processes increase the quality of concentrate (for example during removal of copper from molybdenite concentrates).
In purification and enrichment processes of solutions, leaching processes are not necessarily selective and consequently produce leaching solutions containing, besides the metal of interest, a range of impurities. This, added to the fact that concentration of the metal of interest may not be too high, makes direct recovery of the metal of interest from the leaching solution impossible. Accordingly, these solutions must be pre-treated through purification and enrichment steps.
Purification eliminates impurities, effectively isolating valuable elements. Enrichment of solutions is also particularly beneficial for reducing the volumes of solution to be treated in subsequent steps of metal recovery. This decreases investment costs and increases efficiency in recovery.
In the present invention, a process for recovery of molybdenum as molybdenum trioxide, from diluted acid leaching solutions of metallurgic residues, having a high concentration of arsenic, antimony, or bismuth, is disclosed.
The object of the present invention is to recover molybdenum, through ion exchange, contained in diluted leaching solutions containing molybdenum, but having a high concentration of arsenic, among other impurities, in such a manner that a molybdenum product is obtained efficiently and profitably.
Prior art includes documents disclosing molybdenum recovery through ion exchange. Such is the case of U.S. Pat. No. 4,891,067, disclosing a process for selective separation of molybdenum present in an acid solution at pH 2 and containing molybdenum and at least one of the elements in the group consisting of uranium, iron, arsenic, phosphorous, silicon, and vanadium. Such a process comprises contacting the acid solution with a stationary phase consisting of a resin with an active oxime group, and eluting the stationary phase with an alkaline solution to recover molybdenum. U.S. Pat. No. 4,596,701 discloses a procedure for purifying molybdenum trioxide, specifically disclosing a method for preparing ammonium molybdate comprising contacting a concentrate with an aqueous solution of sulfuric acid, ammonium, ammonium sulfate and persulfate, and solubilizing at least 2% of the molybdenum present in the concentrate.
A Chilean patent application CL N° 3137-2005 discloses a process for molybdenum and copper extraction, which are contained in solidified slags from fusion processes in copper concentrates. This document does not interfere with the present patent application since the slag does not contain arsenic, therefore treating a technical problem different to the one addressed in the present patent application.
None of the previously mentioned processes interfere with the present application since such documents of the prior art show processes with different operative variables, and therefore, do not provide the benefits obtained with the present invention, which include efficiently and profitably recovering technical grade MoO3 (molybdenum trioxide) from leaching solutions with high arsenic content. Through the present invention, a technical grade molybdenum trioxide is obtained, which means having a molybdenum content over 58%, and a content of non-regulated metals, such as As, Sb, and Bi, in amounts lower than 0.1%.